T-LYMPHOCYTES

The main cells of the immune system are derived from the lymphoid and myeloid arms of the hematopoietic system. In the bone marrow, the myeloid arm gives rise to peripheral dendritic cells, phagocytes (neutrophils and monocytes), mast cell precursors, basophils, eosinophils, platelets, and erythrocytes. In the tissues, peripheral dendritic cells, monocytes, and mast cell precursors further differentiate. The monocyte can become a macrophage. In the bonemarrow, the lymphoid arm gives rise to NK-cells, B-cells, and pre-T-cells. The pre-Tcells differentiate to T-cells in the thymus. Secondary lymphoid organs, including lymph nodes and the spleen, are areas where antigen presenting cells, B-cells, and dendritic cells, present antigen to T-cells. Terminal differentiation of B- and T-cells also occurs in these organs.